Semiconductor device manufacturing system for etching a semiconductor by plasma discharge

ABSTRACT

A semiconductor device manufacturing system has a vacuum chamber which is provided with a cathode electrode for holding a substrate to be processed and into which a reactive gas for generating discharging plasma by the application of a high-frequency electric power is introduced, a measuring circuit which measures at least one of the impedance of a system including the plasma, the peak-to-peak voltage of a high-frequency signal applied to the plasma, and a self-bias voltage applied to the cathode electrode, and a sense circuit which compares the measured value from the measuring circuit with previously prepared data and senses the change of processing characteristics with time for the substrate in using the discharging plasma or the cleaning time of the inside of the vacuum chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 09/527,681, filed Mar. 17,2000, now U.S. Pat. No. 6,685,797 which is incorporated herein byreference.

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 11-076352, filed Mar. 19,1999, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a semiconductor device manufacturing system,and more particularly to a system for processing a semiconductorsubstrate by plasma discharge used in, for example, a reactive ionetching (RIE) system with a high-frequency power supply.

In a dry etching system used in the process of manufacturingsemiconductor devices, a substrate on whose surface a given mask patternhas been formed is placed in a vacuum reactive chamber. A reactive gasis introduced into the vacuum reactive chamber and at the same time,discharging plasma is generated, thereby causing reactive ions to etchthe substrate.

At that time, high-vapor-pressure reaction products are generallyproduced as a result of the reaction between the reactive ions and theetched layer. The reaction products are exhausted. Depending on thepressure in the vacuum chamber, the type of reactive gas, the flow rate,and the amount of energy of the reactive ions, the rate of reaction withthe etched film and the types of reaction products differ.

In a system for processing a semiconductor substrate by plasmadischarge, one means for clearly verifying the presence or absence ofthe change of processing conditions with time and the degree of thechange with time, if any, is to process a substrate in such a mannerthat it has a shape with a high aspect ratio.

The shape with a high aspect ratio is, for example, a contact hole, avia hole, or a trench. As a typical example, problems encountered in acase where a conventional dry etching system is used in the process offorming trenches for trench capacitors in the memory cells of, forexample, a DRAM will be explained.

FIGS. 1A and 1B are sectional views of a substrate in the process offorming a trench for trench capacitor.

As shown in FIG. 1A, a TEOS (Tetraethyl orthosilicate) film 12 is firstformed on an Si substrate 11 to be processed. Then, patterning is doneto form a mask pattern, thereby forming a sample of the substrate.

Next, after each lot processing of semiconductor substrates by amagnetron RIE system, a sample of the substrate as shown in FIG. 1A isplaced in a vacuum reactive chamber. Reactive gases HBr, O₂, and NF₃ areintroduced into the vacuum reactive chamber at flow rates of 100, 10,and 70 sccm, respectively. Then, plasma discharge is effected at apressure of about 200 mTorr (about 26.6 Pa) with a high-frequency powersupply output of about 1000 W, thereby causing reactive ions to etch thesample.

As a result of this, a trench 13 for trench capacitor is formed at theSi substrate 11 as shown in FIG. 1B. Here, θ is the taper angle at thetop of the trench 13 and D is the diameter of the bottom of the trench.

FIG. 2 shows the relationship between the number of lots of substratesprocessed by a conventional RIE system and the diameter D (μm) of thetrench bottom. The number of substrates processed in one lot is, forexample, 24 to 25.

As seen from FIG. 2, as the number of substrates processed increases,the diameter D of the trench bottom decreases. The reason is that, asthe number of substrates processed increases, the degree of the taper atthe top of the trench decreases, making the taper angle θ smallergradually.

The cause of this is not clear, but the following phenomenon isconsidered to be taking place.

In processing a trench for trench capacitor, SiBr_(x), SiBr_(y)O_(z),and SiF_(α) are mainly produced as reaction products. Although most ofthem are exhausted, part of them adhere to the relativelylow-temperature parts of the vacuum chamber or decompose again intosubstances with lower vapor pressures and adhere to the inside of thevacuum chamber.

These deposits are estimated to be of the SiO₂ family. When the depositsbuild up to form a film, they are exposed to degassing or plasma, whichcauses the film to decompose again. As a result, the actual flow rate ofeach process gas in the atmosphere in the vacuum chamber differs fromthe set flow rate, preventing the desired shape and etching rate frombeing achieved.

As described above, because the diameter of the trench bottom is closelyrelated to the condition of the deposited film on the inside of thevacuum chamber, a grasp of the condition of the deposited film wouldhelp determine the time the inside of the vacuum chamber should becleaned. It is, however, impossible to grasp the condition of the innersurface of the vacuum chamber from the outside.

At present, the standard value of the diameter D of the trench bottomfor trench capacitor is 0.1 μm. In this situation, the vacuum chamber isopened to atmosphere and cleaned manually every, for example, eight lotson the basis of the data in FIG. 2. However, it is not clear whether themethod is the best.

As described above, with the conventional dry etching system formanufacturing semiconductor devices, it is impossible to externallygrasp the condition of the inner surface and others of the vacuumchamber. For example, in processing a trench for trench capacitor, thechange of the diameter of the trench bottom with time dependent on thenumber of substrates processed is impossible to grasp and therefore thesuitable cleaning time of the inside of the vacuum chamber cannot bedetermined.

BRIEF SUMMARY OF THE INVENTION

It is, accordingly, an object of the prevention is to provide asemiconductor device manufacturing system which enables the change ofthe diameter of the trench bottom with time dependent on the number ofsubstrates processed in processing a trench and the condition of theinner surface and others of the vacuum chamber to be grasped from theoutside, making it possible to determine the suitable cleaning time ofthe inner surface of the vacuum chamber and control the processing ofthe shape of a substrate, which thereby suppresses the change with time.

According to a first aspect of the present invention, there is provideda semiconductor device manufacturing system comprising: a vacuum chamberprovided with a cathode electrode for holding a substrate to beprocessed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; a measuring circuit connected to the cathode electrode, formeasuring at least one of the impedance of a system including theplasma, the peak-to-peak voltage of a high-frequency signal applied tothe plasma, and a self-bias voltage applied to the cathode electrode;and a sense circuit for receiving the measured value from the measuringcircuit, and for sensing the change of processing characteristics withtime for the substrate in using the discharging plasma by comparing themeasured value with previously prepared data.

According to a second aspect of the present invention, there is provideda semiconductor device manufacturing system comprising: a vacuum chamberprovided with a cathode electrode for holding a substrate to beprocessed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; a measuring circuit connected to the cathode electrode, formeasuring at least one of the impedance of a system including theplasma, the peak-to-peak voltage of a high-frequency signal applied tothe plasma, and a self-bias voltage applied to the cathode electrode;and a control circuit for receiving the measured value from themeasuring circuit, for supplying an output based on the measured valueto the high-frequency power supply, and for controlling the output ofthe high-frequency power supply in such a manner that the measured valueof the measuring circuit is kept at a specific value.

According to a third aspect of the present invention, there is provideda semiconductor device manufacturing system comprising: a vacuum chamberprovided with a cathode electrode for holding a substrate to beprocessed and a reactive gas intake and into which a reactive gas forgenerating discharging plasma by the application of a high-frequencyelectric power is introduced through the intake; a high-frequency powersupply connected to the cathode electrode, for applying a high-frequencyelectric power to the cathode electrode; a valve provided at the intakein such a manner that the intake of the reactive gas introduced into thevacuum chamber is controlled; a measuring circuit connected to thecathode electrode for measuring at least one of the impedance of asystem including the plasma, the peak-to-peak voltage of ahigh-frequency signal applied to the plasma, and a self-bias voltageapplied to the cathode electrode; and a control circuit for receivingthe measured value from the measuring circuit, for supplying an outputbased on the measured value to the valve, and for controlling theoperation of the valve in such a manner that the measured value of themeasuring circuit is kept at a specific value.

According to a fourth aspect of the present invention, there is provideda semiconductor device manufacturing system comprising: a vacuum chamberprovided with a cathode electrode for holding a substrate to beprocessed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; a measuring circuit for measuring at least one of theimpedance of a system including the plasma, the peak-to-peak voltage ofa high-frequency signal applied to the plasma, and a self-bias voltageapplied to the cathode electrode; and a report circuit for receiving themeasured value from the measuring circuit, for sensing that the measuredvalue has departed from a preset range, and for reporting the cleaningtime of the inside of the vacuum chamber.

According to a fifth aspect of the present invention, there is provideda semiconductor device manufacturing system comprising: a vacuum chamberprovided with a cathode electrode for holding a substrate to beprocessed, a reactive gas intake, and a reactive gas outlet, and intowhich a reactive gas for generating discharging plasma by theapplication of a high-frequency electric power is introduced through theintake; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; an electronic valve provided at the outlet in such a mannerthat the pressure in the vacuum chamber is adjusted; a measuring circuitconnected to the cathode electrode for measuring at least one of theimpedance of a system including the plasma, the peak-to-peak voltage ofa high-frequency signal applied to the plasma, and a self-bias voltageapplied to the cathode electrode; and a control circuit for receivingthe measured value from the measuring circuit, for supplying an outputbased on the measured value to the valve, and for controlling theoperation of the valve in such a manner that the measured value of themeasuring circuit is kept at a specific value.

According to a sixth aspect of the present invention, there is provideda semiconductor device manufacturing system comprising: a vacuum chamberprovided with a cathode electrode for holding a substrate to beprocessed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to the cathodeelectrode, for applying a high-frequency electric power to the cathodeelectrode; a cooling gas carrying path provided at the cathode electrodeand into which a cooling gas is introduced to cool the substrate; anelectronic valve provided at the cooling gas carrying path in such amanner that the pressure of the cooling gas introduced into the coolinggas carrying path is adjusted; a measuring circuit connected to thecathode electrode, for measuring at least one of the impedance of asystem including the plasma, the peak-to-peak voltage of ahigh-frequency signal applied to the plasma, and a self-bias voltageapplied to the cathode electrode; and a control circuit for receivingthe measured value from the measuring circuit, for supplying an outputbased on the measured value, and for controlling the operation of thevalve in such a manner that the measured value of the measuring circuitis kept at a specific value.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIGS. 1A and 1B are sectional views of a substrate in the process offorming a trench for trench capacitor;

FIG. 2 shows the relationship between the number of substrates processedand the diameter of the trench bottom in a conventional dry etchingsystem;

FIG. 3 is a schematic block diagram showing the configuration of an RIEsystem according to a first embodiment of the present invention and itsperipheral circuit;

FIG. 4A shows the relationship between the number of lots of substratesprocessed, the peak-to-peak voltage of a high-frequency signal, and thediameter of the trench bottom in the system of FIG. 3;

FIG. 4B shows the relationship between the peak-to-peak voltage of thehigh-frequency signal and the diameter of the trench bottom in thesystem of FIG. 3;

FIG. 5 is a schematic block diagram showing the configuration of an RIEsystem according to a second embodiment of the present invention and itsperipheral circuit;

FIG. 6A shows the relationship between the output of a high-frequencypower supply and the peak-to-peak voltage of the high-frequency signalin the system of FIG. 5;

FIG. 6B shows the relationship between the peak-to-peak voltage of thehigh-frequency signal and the taper angle θ at the top of the trench inthe system of FIG. 5;

FIG. 7 is a schematic block diagram showing the configuration of an RIEsystem according to a third embodiment of the present invention and itsperipheral circuit;

FIG. 8A shows the relationship between the flow rate of a reactive gasand the peak-to-peak voltage of a high-frequency signal in the system ofFIG. 7;

FIG. 8B shows the relationship between the peak-to-peak voltage of thehigh-frequency signal and the taper angle at the top of the trench inthe system of FIG. 7;

FIG. 9 is a flowchart to help explain a method of manufacturingsemiconductor devices using the system of FIG. 5 or 7;

FIG. 10 is a schematic block diagram showing the configuration of an RIEsystem according to a fourth embodiment of the present invention and itsperipheral circuit;

FIG. 11 shows the relationship between the pressure in the vacuumreactive chamber and the taper angle θ at the top of the trench in thesystem of FIG. 10;

FIG. 12 is a schematic block diagram showing the configuration of an RIEsystem according to a fifth embodiment of the present invention and itsperipheral circuit; and

FIG. 13 shows the relationship between the pressure of a cooling gas toadjust the temperature of the substrate to be processed and the taperangle at the top of the trench in the system of FIG. 12.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, referring to the accompanying drawings, embodiments of thepresent invention will be explained. The same reference symbolsdesignate the corresponding parts throughout all the views andrepetitious explanation will be avoided.

FIG. 3 shows a magnetron RIE system, a type of dry etching systemaccording to a first embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

In FIG. 3, numeral 20 indicates an RIE system. The RIE system 20 isprovided with a vacuum reactive chamber 21. In the vacuum reactivechamber 21, a cathode electrode 23 for holding a substrate to beprocessed is provided. When a high-frequency power supply, explainedlater, applies a high-frequency electric power to the cathode electrode23 and a reactive gas is introduced, discharging plasma 24 developsinside the vacuum reactive chamber 21. In the vacuum reactive chamber21, a gas intake 25 for introducing a reactive gas and an outlet 26 forexhausting the gas from the vacuum reactive chamber 21 are provided.Three branch paths 27, 28, 29 are provided at the gas intake 25. When amixed gas of three types of gases, for example, HBr, O₂, and NF₃, isused as etching gas, these three types of gases are carried through thethree branch paths 27, 28, 29. In the branch paths 27, 28, 29,electronic valves 30, 31, 32 for adjusting the flow rate of the gasesare provided respectively. At the outlet 26, there is provided anelectronic valve 33 for controlling the amount of exhaust to adjust thepressure in the vacuum reactive chamber 21.

A high-frequency power supply 34 including, for example, a magnetron isconnected to the cathode electrode 23. The output of the high-frequencypower supply 34 is supplied to the cathode electrode 23. An impedancematching circuit (or matching controller) 35 is provided between thehigh-frequency power supply 34 and the cathode electrode 23. Thematching controller 35 is for effecting the impedance matching betweenthe output of the high-frequency power supply 34 and the load side.

The matching controller 35 is composed of, for example, two variablecapacitors 36, 37, and an inductance 38. The values of the two variablecapacitors 36, 37 are controlled automatically by an automatic controlloop (not shown) in such a manner that the reflected power returning tothe high-frequency power supply 34 always becomes the smallest, therebyachieving impedance matching.

Further connected to the cathode electrode 23 are a Vpp measuringcircuit 39 for measuring the peak-to-peak voltage Vpp of ahigh-frequency signal applied to the plasma 24, a Vdc measuring circuit40 for measuring a self-bias voltage Vdc applied to the cathodeelectrode 23, and an impedance (Z) measuring circuit 41 for measuringthe impedance (Z) of a system including the plasma 24.

Then, the voltage Vpp measured at the Vpp measuring circuit 39, thevoltage Vdc measured at the Vdc measuring circuit 40, and the impedance(Z) measured at the impedance measuring circuit 41 are inputted to asense/report circuit 42. The sense/report circuit 42 has the function ofcomparing the outputs (or measurements) of the Vpp measuring circuit 39,the Vdc measuring circuit 40, and the impedance measuring circuit 41with previously prepared data, sensing the change of processingcharacteristics with time for the substrate 22 to be processed, anddetermining and reporting the cleaning time of the inside of the vacuumchamber 21, and outputs a sense signal and a report signal.

The matching controller 35 is so controlled that the total of impedanceas a physical quantity to be monitored is, for example, 50Ω in the partincluding the matching controller 34 and beyond that when viewed fromthe high-frequency power supply 34, that is, the system including theplasma on the vacuum reactive chamber 21 side. For example, if theimpedance of the system including the plasma is 30Ω, the values of thetwo capacitors 36, 37 are adjusted by the automatic control loop so thatthe impedance of the matching controller 35 itself may be 20Ω. Since theimpedance of the system including the plasma varies, depending on theetching condition of the substrate in etching the substrate or thechange of the state in the vacuum reactive chamber 21, it is possible tocontrol of the shape of the substrate and grasp the buildup of thedeposited film on the inner surface of the vacuum reactive chamber 21 onthe basis of the result of monitoring the impedance of the systemincluding the plasma.

Ordinary lot processing was done using the RIE system in FIG. 3. Aftereach lot process, a sample of the substrate as shown in FIG. 1A wasplaced in the vacuum reactive chamber 21. HBr gas, O₂ gas, and NF₃ gaswere introduced as reactive gases into the vacuum reactive chamber atflow rates of about 100, 10, and 70 sccm, respectively. Dischargingplasma 24 was generated at a pressure of about 200 mToor (about 26.6 Pa)in the vacuum reactive chamber with the high-frequency power supply 34outputting about 1000 W, thereby causing reactive ions to etch thesample. As a result, a trench 13 for trench capacitor was formed in theSi substrate 11 as shown in FIG. 1B.

At that time, the relationship between the number of lots of substratesprocessed and the diameter D of the trench bottom in the RIE system wasexamined. In addition, the relationship between the number of lotsprocessed and the peak-to-peak voltage Vpp of a high-frequency signalapplied to the cathode electrode 23 in the vacuum reactive chamber wasexamined. The results of these are shown in FIG. 4A.

Examinations as described above were made several times using the samemask pattern under the same etching conditions. FIG. 4B shows the resultof examining the relationship between the peak-to-peak voltage Vpp ofthe high-frequency signal at that time and the diameter D of the trenchbottom.

It can be seen from FIGS. 4A and 4B that there is a correlation betweenthe diameter D of the trench bottom and the peak-to-peak voltage Vpp ofthe high-frequency signal and the diameter D of the trench bottom can bealmost determined by measuring the Vpp with the Vpp measuring circuit39.

As described above, the reason why the diameter D of the trench bottomcorrelates with the peak-to-peak voltage Vpp of the high-frequencysignal is not clear, but can be considered as follows.

When the shape of the trench has got thinner for some reason, theopening area of the Si substrate to be etched decreases. Because themain reaction products are estimated to be SiBr_(x), SiBr_(y)O_(z),SiF_(α), and the like, as the amount of Si in the substance to be etcheddecreases, the amount of reaction products decreases accordingly. As aresult, the frequency of collision between ions and reaction productsdecreases, resulting in a decrease in the impedance of the systemincluding the plasma 24. If the output of the high-frequency powersupply is W, the equation W=Vpp²/Z holds. In this case, because W isconstant (in this embodiment, about 1000 W), Vpp is also expected todecrease.

Between the self-bias voltage Vdc applied to the cathode electrode 23holding the substrate 22 and the peak-to-peak voltage Vpp of thehigh-frequency signal, the fact that Vdc is almost equal to Vpp/2 isgenerally true. As a result, it is easily estimated that the diameter Dof the trench bottom is determined by measuring the Vdc with the Vdcmeasuring circuit 40 as is the Vpp.

With the RIE system of the first embodiment, there is provided thesense/report circuit 42 that compares the outputs (measurements) of themeasuring circuits 39, 40, and 41 with the previously prepared data andsenses and reports the change of processing characteristics with timefor a substrate to be processed or the cleaning time of the inside ofthe vacuum reactive chamber. The sense signal makes it possible toexternally grasp the change of the diameter of the trench bottomdependent on the number of substrates processed in processing a trenchfor trench capacitor. Furthermore, the report signal enables thecondition and the like of the inner surface of the vacuum reactivechamber to be grasped indirectly from the outside, which makes itpossible to determine the suitable cleaning time of the inside of thevacuum reactive chamber.

FIG. 5 shows a magnetron RIE system, a type of dry etching systemaccording to a second embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

The RIE system of the second embodiment differs from that of FIG. 3 inan additional high-frequency power supply control circuit 43 thatreceives the sense signal outputted from the sense/report circuit 42 andcontrols the output of the high-frequency power supply 34.

In the RIE system of the second embodiment, on the basis of the sensesignal outputted according to one or two or more of the value of Vppmeasured by the Vpp measuring circuit 39, the value of Vdc measured bythe Vdc measuring circuit 40, and the value of the impedance measured bythe Z measuring circuit 41, the high-frequency power supply controlcircuit 43 is controlled. In addition, the output of the high-frequencypower supply 34 is controlled on the basis of the output of thehigh-frequency power supply control circuit 43. In this way, theimpedance Z, the peak-to-peak voltage Vpp of the high-frequency electricpower, and the self-bias voltage Vdc are controlled. Then, shape controlin processing a substrate can be performed by controlling the output ofthe high-frequency power supply 34 in such a manner that each of themeasured values is kept at a desired constant value.

After each lot processing of semiconductor substrates was carried outusing the RIE system of FIG. 5, a sample of the substrate as shown inFIG. 1A was placed in the vacuum reactive chamber. HBr gas, O₂ gas, andNF₃ gas were introduced as reactive gases through the branch paths 27,28, 29 into the vacuum reactive chamber at flow rates of about 100, 10,and 70 sccm, respectively. Discharging plasma 24 was generated at apressure of about 200 mToor (about 26.6 Pa) in the vacuum reactivechamber with the output of the high-frequency power supply 34 beingapplied to the cathode electrode 23, thereby causing reactive ions toetch the sample.

At that time, dry etching was done changing the output (RF-Power) (W) ofthe high-frequency power supply 34, thereby examining how thepeak-to-peak voltage Vpp of the high-frequency signal changed. At thesame time, how the taper angle θ at the top of the trench as shown inFIG. 1B changed was also examined. The results are shown in FIGS. 6A and6B.

It can be seen from FIGS. 6A and 6B that the output of thehigh-frequency power supply 34 and the peak-to-peak voltage Vpp of thehigh-frequency signal and the taper angle θ of the trench haveone-to-one correspondence and therefore the taper angle θ can becontrolled by the high-frequency output.

The reason is not clear. The equation W=Vpp²/Z generally holds. When theamount of reaction products generated is almost constant, Z is almostconstant. Therefore, Vpp is proportional to W and the value of Vpp isestimated to be determined.

Furthermore, part of the reaction products adhere to the sidewall of thetrench to make a sidewall protective film. The taper angle θ at the topof the trench is controlled by the amount of the sidewall protectivefilm. As the sidewall protective film gets thicker, the taper angle θbecomes smaller.

In addition, since Vdc is generally equal to Vpp/2, an increase in Vppincreases Vdc, which increases the energy at which reactive ions arriveat the substrate. As a result, the sidewall protective film inside thetrench is estimated to be scraped away, making the taper stand morestraight.

With the RIE system of the second embodiment, the value of Vpp ismeasured by the Vpp measuring circuit 39, the value of Vdc is measuredby the Vdc measuring circuit 40, and the value of Z is measured by the Zmeasuring circuit 41. The high-frequency power supply control circuit 43is controlled on the basis of the sense signal outputted from thesense/report circuit 42 according to the result of the measurements. Theoutput of the high-frequency power supply 34 is controlled to anarbitrary value in such a manner that the measured value of Vpp, Vdc, orZ is kept at a specific set value. Controlling the high-frequency powersupply circuit 43 and the output of the high-frequency power supply 34this way enables the shape of the trench to be controlled.

FIG. 7 shows a magnetron RIE system, a type of dry etching systemaccording to a third embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

The RIE system of the third embodiment differs from that of FIG. 1 in anadditional gas flow-rate control circuit 44 that receives the sensesignal outputted from the sense/report circuit 42 and controls the flowrate of each of the gases by controlling the opening and closing of theelectronic valves 30, 31, 32. The output of the gas flow-rate controlcircuit 44 is supplied to each of the electronic valves 30, 31, 32.

In the RIE system constructed as described above, after each lotprocessing of semiconductor substrates, a sample of the substrate asshown in FIG. 1A was placed in the vacuum reactive chamber. HBr gas, O₂gas, and NF₃ gas were introduced as reactive gases through the branchpaths 27, 28, 29 into the vacuum reactive chamber. Discharging plasma 24was generated at a pressure of about 200 mToor (about 26.6 Pa) in thevacuum reactive chamber with the output (RF-Power) of the high-frequencypower supply 34 being applied to the cathode electrode 23, therebycausing reactive ions to etch the sample.

At that time, dry etching was done by introducing HBr gas and NF₃ gas atflow rates of about 100 and 70 sccm respectively, and changing a flowrate of O₂ gas, thereby examining how the peak-to-peak voltage Vpp ofthe high-frequency signal changed. At the same time, how the taper angleθ at the top of the trench as shown in FIG. 1B changed was alsoexamined. The results are shown in FIGS. 8A and 8B.

It can be seen from FIGS. 8A and 8B that the flow rate of the O₂ gas andthe peak-to-peak voltage Vpp of the high-frequency signal and the taperangle θ of the trench have one-to-one correspondence and thereforecontrol can be performed on the basis of the flow rate of the O₂ gas.

The reason is not clear. The equation W=Vpp²/Z generally holds. Anincrease in the flow rate of the O₂ gas increases the amount of reactionproducts of the SiBryO₂ family generated, which increases the impedanceZ. In this case, therefore, W is almost constant. From this, the valueof Vpp can be considered to have decreased.

Furthermore, since the magnitude of the impedance Z depends on theamount of reaction products, a similar effect is easily estimated to beproduced in a case where a process gas including a bromine-containinggas, such as HBr containing Br and F composing reaction products and afluorine-containing gas, such as NF₃, is used.

With the RIE system of the third embodiment, the value of Vpp ismeasured by the Vpp measuring circuit 39, the value of Vdc is measuredby the Vdc measuring circuit 40, and the value of Z is measured by the Zmeasuring circuit 41. On the basis of the results of the measurements,the gas flow-rate control circuit 44 is controlled and the valves 30 to32, particularly the valve 31 for controlling the flow rate of O₂ gas,are controlled. In this way, the flow rate of each process gas iscontrolled to an arbitrary value in such a manner that the measuredvalue of Vpp, Vdc, or Z is kept at a specific set value, which enablesthe shape of the trench to be controlled.

Next, a method of processing a substrate using the RIE system in FIG. 5or 7 will be explained briefly by reference to a flowchart in FIG. 9.

When the processing of a substrate is started, the supply of eachprocess gas and the output of the high-frequency power supply are firststarted.

At least one of the measured values of the impedance Z of the partincluding the system and plasma 24, the peak-to-peak voltage Vpp of thehigh-frequency signal applied to the plasma 24, and the self-biasvoltage Vdc developing at the cathode electrode 23 is taken in by thesense/report circuit 42.

Then, it is judged whether those measured values are equal to thepreviously set values. The judgment is made at the sense/report circuit42. If the measured value is equal to the set value, the supply of theprocess gas and the output of the high-frequency power supply arestopped at the time when the set process end time has been reached,which completes the process.

When the set process end time has not been reached, the measured valueis taken in again by the sense/report circuit 42, which judges whetherthe measured value is equal to the set value.

If the measured value is different from the set value, the processcondition, such as the process gas or the output of the high-frequencypower supply, is adjusted in real time. Then, it is judged whether ameasured value equal to the set value has been obtained. At this time.If a measured value equal to the set value has not be obtained, aprocess stop signal is transmitted to the high-frequency power supply 34or valves 30 to 32, which forces the process to end. At the same time,the sense/report circuit 42 outputs the report signal that reports thatthe cleaning time has been reached.

Monitoring the impedance Z, peak voltage Vpp, and self-bias voltage Vdcmakes it possible to clearly grasp, from the outside of the vacuumchamber, the change of substrate processing characteristic in the vacuumchamber with time and the cleaning time of the inside of the vacuumchamber. In addition, keeping the result of monitoring at an arbitraryvalue enables shape control of processing, which makes it possible tosuppress the change with time.

FIG. 10 shows a magnetron RIE system, a type of dry etching systemaccording to a fourth embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

The RIE system of the fourth embodiment differs from that of FIG. 1 inan additional pressure control circuit 45 that receives the sense signaloutputted from the sense/report circuit 42 and controls the pressure inthe vacuum reactive chamber by controlling the opening and closing ofthe electronic valve 33 provided at the outlet 26. The output of thepressure control circuit 45 is supplied to the valve 33.

After each lot processing of semiconductor substrates using the RIEsystem of the fourth embodiment, a sample of the substrate as shown inFIG. 1A was placed in the vacuum reactive chamber 21. Reactive gas wasintroduced into the vacuum reactive chamber 21. Then, the inside of thevacuum reactive chamber was kept at a specific pressure and the outputof the high-frequency power supply 34 was applied, thereby generatingdischarging plasma 24, which: causes reactive ions to etch the sample.

At that time, dry etching was done changing the pressure in the vacuumreactive chamber 21, thereby examining how the taper angle θ at the topof the trench as shown in FIG. 1A changed. The results are shown inTABLE 1 and FIG. 11.

TABLE 1 PRESSURE (mTorr) TAPER ANGLE θ (°) 100 88.42 150 88.17 200 88.09

It can be seen from TABLE 1 and FIG. 11 that as the pressure in thevacuum reactive chamber 21 decreases, the taper angle θ increases. Thereason is considered as follows. As the pressure in the vacuum reactivechamber decreases, ions begin to have the same direction and thefrequency of collision between ions or between ions and other particles,such as atoms, decreases. As a result, because the kinetic energyaccelerated by an electric field is not lost because of collisions, theenergy at which ions arrive at the substrate increases, which producesthe effect of scraping the sidewall protective film easily as when theoutput of the high-frequency power supply 34 is increased.

Therefore, the taper angle θ can be controlled to a desired value byinputting the sense signal from the sense/report circuit 42 to thepressure control circuit 45, adjusting the amount of exhaust from thevacuum reactive chamber 21 by controlling the opening and closing of thevalve 33 according to the output of the pressure control circuit 45,thereby adjusting and keeping the pressure in the vacuum reactivechamber 21 at a desired constant value.

FIG. 12 shows a magnetron RIE system, a type of dry etching systemaccording to a fifth embodiment of the present invention, and a controlcircuit for controlling the operation of the system.

In the RIE system of the fifth embodiment, a cooling gas intake 51 isprovided on the reverse side of the cathode electrode 23, or on theopposite side to the surface on which a substrate 22 to be processed isplaced. A cooling gas, such as He gas, is introduced through the intake51. The cooling gas introduced through the intake 51 erupts from thesurface of the cathode electrode 23 on which the substrate 22 is placed,thereby cooling the substrate 22.

Furthermore, an electronic valve 52 for adjusting the flow rate of thecooling gas introduced through the intake 51 is provided at the coolinggas intake 51. The opening and closing of the valve 52 is controlledaccording to the output of the gas flow-rate control circuit 53 thatreceives the sense signal outputted from the sense/report circuit 42. Ingeneral, the inside of the vacuum reactive chamber 21 where dischargingplasma is being generated is as high as about 120° C. The substrate 22in the chamber is also at about the same temperature. When a coolinggas, such as He gas, is erupted toward the back of the substrate 22, thetemperature of the substrate 22 is adjusted according to the flow rateof the cooling gas.

After each lot processing of semiconductor substrates using the RIEsystem of the fifth embodiment, a sample of the substrate as shown inFIG. 1A was placed in the vacuum reactive chamber 21. Reactive gas wasintroduced into the vacuum reactive chamber 21. Then, the vacuumreactive chamber was kept at a specific pressure and the cooling gas wasintroduced through the valve 52, thereby lowering the temperature of thesubstrate 22 to a specific temperature. Thereafter, the output of thehigh-frequency power supply 34 was applied to the cathode electrode 23,thereby generating discharging plasma 24, which causes reactive ions toetch the sample.

At that time, dry etching was done changing the temperature of thesubstrate 22, thereby examining how the taper angle θ at the top of thetrench as shown in FIG. 1B changed. The results are shown in TABLE 2 andFIG. 13. The flow rate (pressure) of the cooling gas is shown as thevalues related to the temperature.

TABLE 2 PRESSURE (Torr) TAPER ANGLE θ (°) 10 88.36 15 88.25 20 88.19

It can be seen from TABLE 2 and FIG. 13 that, as the pressure of thecooling gas increases, the taper angle θ increases. The reason isconsidered as follows. As the pressure of the cooling gas is increased,the temperature of the substrate drops, increasing the amount ofdeposits of reaction products (sediment and sidewall protective films),which produces the effect of decreasing the taper angle θ as when theflow rate of O₂ gas is increased.

Therefore, the taper angle θ can be controlled to a desired value byadjusting and keeping the temperature of the substrate at a desiredconstant value.

As described above, with a semiconductor device manufacturing systemaccording to the present invention, it is possible to externally graspthe change of the diameter of the trench bottom with time dependent onthe number of substrates processed in processing, for example, a trenchfor trench capacitor and the condition of the inner surface and othersof the vacuum reactive chamber, making it possible to determine thesuitable cleaning time of the inside of the vacuum reactive chamber andcontrol the processing of the shape of a substrate, which therebysuppresses the change with time.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended and their equivalents.

1. A semiconductor device manufacturing system comprising: a vacuumchamber provided with a cathode electrode for holding a substrate to beprocessed and into which a reactive gas for generating dischargingplasma by the application of a high-frequency electric power isintroduced; a high-frequency power supply connected to said cathodeelectrode, for applying a high-frequency electric power to said cathodeelectrode; a cooling gas carrying path provided at said cathodeelectrode and into which a cooling gas is introduced to cool saidsubstrate; an electronic valve provided at said cooling gas carryingpath in such a manner that the pressure of said cooling gas introducedinto said cooling gas carrying path is adjusted; a measuring circuitconnected to said cathode electrode, for measuring at least one of theimpedance of a system including said plasma, the peak-to-peak voltage ofa high-frequency signal applied to said plasma, and a self-bias voltageapplied to said cathode electrode; and a control circuit for receivingthe measured value from said measuring circuit, for supplying an outputbased on said measured value, and for controlling the operation of saidvalve in such a manner that the measured value of said measuring circuitis kept at a specific value.
 2. The system according to claim 1, whereinsaid reactive gas is an etching gas for etching said substrate to beprocessed.
 3. The system according to claim 1, further comprising animpedance matching circuit provided between said high-frequency powersupply and said cathode electrode of said vacuum chamber, for effectingthe impedance matching between the output of said high-frequency powersupply and a load on the high-frequency power supply.